National health examination surveys; a source of critical data

Abstract The aim of this paper is to contribute technical arguments to the debate about the importance of health examination surveys and their continued use during the post-pandemic health financing crisis, and in the context of a technological innovation boom that offers new ways of collecting and analysing individual health data (e.g. artificial intelligence). Technical considerations demonstrate that health examination surveys make an irreplaceable contribution to the local availability of primary health data that can be used in a range of further studies (e.g. normative, burden-of-disease, care cascade, cost and policy impact studies) essential for informing several phases of the health planning cycle (e.g. surveillance, prioritization, resource mobilization and policy development). Examples of the use of health examination survey data in the World Health Organization (WHO) European Region (i.e. Finland, Italy, Malta and the United Kingdom of Great Britain and Northern Ireland) and the WHO Region of the Americas (i.e. Chile, Mexico, Peru and the United States of America) are presented, and reasons why health provider-led data cannot replace health examination survey data are discussed (e.g. underestimation of morbidity and susceptibility to bias). In addition, the importance of having nationally representative random samples of the general population is highlighted and we argue that health examination surveys make a critical contribution to external quality control for a country’s health system by increasing the transparency and accountability of health spending. Finally, we consider future technological advances that can improve survey fieldwork and suggest ways of ensuring health examination surveys are sustainable in low-resource settings.


Introduction
National health examination surveys have been developed to gather important information that cannot be obtained from other sources.In these surveys, trained field staff take objective, biophysical measurements (e.g. of anthropometric variables or blood pressure) and collect biological samples (e.g. of blood or urine) for laboratory analysis.The data obtained complement the self-reported data collected, for example, by health interview surveys, which include only self-reported information.In addition, health examination surveys are the observational studies with the greatest external validity because they are based on randomized, representative household samples.Consequently, the information obtained is relevant for both population (i.e.public health) and individual health. 1 Health examination surveys provide more accurate information than health interview surveys.For example, people tend to overestimate their height and underestimate their weight compared with measurements taken by trained staff, which results in underestimates of their body mass index -a measure widely used for assessing people for obesity and for predicting morbidity from several chronic noncommunicable diseases. 2,3ost high-and middle-income countries conduct national health interview surveys that use questionnaires to collect basic information about the general population.For European Union member states, European health interview surveys are mandatory. 4Far fewer countries regularly conduct health examination surveys.Nevertheless, many low-and middle-income countries have conducted at least one small health examination survey in accordance with the World Health Organization (WHO) STEPwise approach to noncommunicable disease risk factor surveillance, known as STEPS. 5n addition, many low-and middle-income countries conduct Demographic and Health Surveys (DHS), which are funded by the United States Agency for International Development, at least every 5 years and some (e.g.Peru) conduct them annually.These surveys include a small number of biophysical assessments, such as anthropometry and anaemia testing.6 However, few countries have a track record of frequent health examination surveys that include a wide range of biophysical measurements.The longest running health examination survey series in Europe has been conducted by Finland every 5 years since 1972 (i.e. the national FINRISK study).7 In the United States of America, National Health and Nutrition Examination Surveys started in the 1960s and have been run as a continuous programme since 1999.8 Existing national health examination surveys differ in the age groups covered, the range of measurements taken and the way they are organized.For example, most health examination surveys in mainland Europe and the United States make use of clinical examination centres, whereas those in the United Kingdom of Great Britain and Northern Ireland and Latin America involve visiting participants in their own homes.9,10 Despite some differences, they share many features, particularly sampling methods, survey questions, anthropo-metric measurements and some other biophysical measurement protocols.1,9,10 Although numerous reports and scientific papers have described findings based on health examination survey data, which implicitly suggests they are valuable data sources, few countries conduct regular, nationally representative, wide-ranging health examination surveys.Moreover, many countries that do conduct regular health examination surveys are struggling to secure longterm financing for successive surveys.Countries with small populations face additional challenges, including a lack of infrastructure and resources for conducting regular, nationally representative health examination surveys.11 Recently, several health examination surveys around the world have been delayed, survey field costs have risen and financing has been cut.In addition, advances in medical informatics and artificial intelligence have given rise to doubts about whether health examination surveys provide the most efficient means of collecting data.Apart from a few studies from Chile, England and Finland, [12][13][14][15] little has been published on the usefulness of health examination surveys, their impact or factors influencing their effectiveness.In this context, it is possible to ask: (i) whether random general population samples are still needed for chronic disease surveillance and health planning; (ii) whether governments should still finance costly population health surveys; and (iii) whether new information technology could be used to generate chronic disease indicators that replace the field measurements conducted in health examination surveys.
The aim of this paper was to discuss these questions with reference to technical arguments and to examples drawn from health examination surveys conducted in Chile, England, Finland, Italy, Malta, Mexico, Peru and the United States.

Noncommunicable disease
Health examination surveys can provide primary data for use in different phases of the noncommunicable disease health planning cycle, including surveillance, prioritization, resource mobilization and policy formulation, implementation and impact assessment.
Table 1 shows some traditional noncommunicable disease indicators that can be obtained directly from health examination survey measures, and describes the specific contribution each of these indicators can make to deriving estimates of variables in other studies, such as: (i) studies to establish population norms; (ii) studies of the care cascade and health system performance; (iii) studies of health inequalities; (iv) studies of the burden of disease and of the burden attributable to specific risk factors; (v) studies of health costs and avoidable health costs; and (vi) studies of changes in population trends.Health policies and laws usually cite these studies directly but do not cite health examination surveys, which may hide their importance.In practice, national ministries of health could justify their budgets for health examination surveys by highlighting these contributions, and by giving examples of how health examination survey data can be used in local policy formulation, implementation and assessment.In Chile, health examination survey data have been used to supplement the findings of all the different study types listed in Table 1.
Several noncommunicable disease preventive policies for nutrition, tobacco control and disease management (e.g.so-called WHO best buys) have been supported by, and their impact assessed, using health examination survey data.Examples of the influence of health examination surveys on policy in Chile, England, Finland, Italy, Malta, Mexico, Peru and the United States are described in Table 2 and Table 3.
Data from health examination surveys can also be used to generate local hypotheses on the association between the population's exposure to risk factors and chronic disease, to predict the future disease burden and to influence clinical and lifestyle guideline development (Table 3).

Health policy
Data from health examination surveys can also support public health decisionmaking, including deciding on where policies should be targeted.

Monitoring and establishing norms
Repeated health examination measures can be used to monitor changes in the health status of the population over time, thereby making it possible to determine whether implemented policies are having the desired effects (Table 2 and Table 3).
Even where health examination survey measurements are not used directly, they can contribute to improving other survey data.For example, Public Health England used survey data on height and weight to correct self-reported anthropometric data from the Active People Survey in England and to create an adult excess weight indicator for the Public Health Outcomes Framework. 49he Active People Survey included 1000 telephone participants from each local government area; that level of coverage would be far too expensive for an health examination survey.
Data from health examination surveys have also been used to determine population norms and reference values for diagnostic and laboratory tests (e.g.blood tests for thyroid hormones, liver enzymes and vitamins and urine tests for iodine excretion).Examples are listed in Table 2 and Table 3.

Health spending
Health examination surveys can help improve the transparency and accountability of government health spending.Countries without health examination survey data on basic health indicators often base policy decisions on weak data or on imprecise estimates borrowed from other countries.Moreover, a lack of data makes it almost impossible to evaluate and justify budgets.Among the different branches of government, the health sector has always had the greatest difficulty in demonstrating the social impact of interventions and the efficiency of investments.This lack of evidence may be one reason why some countries have underfinanced health budgets.Serial cross-sectional health examination surveys can help assess trends in health indicators and the impact of policy.Without this information, health spending may lack transparency and accountability, which could affect the population's confidence in the health authority.

Data quality
As the use of health informatics and artificial intelligence to analyse health-care records and administrative health data is increasing, decision-makers could ask, why not replace health examination surveys with these or other data sources?However, the data obtained by Paula Margozzini et al.

Policy & practice
health providers are usually captured using non-standardized formats: for example, different definitions of risk factor exposure or disease may be used and not everyone may be asked the same questions, as is done in surveys.Moreover, people may be receiving treatment simultaneously from different providers.In the noncommunicable disease era in particular, an individual's journey across health and disease states is complex and difficult to register.
Health provider data usually underestimate noncommunicable disease morbidity because they exclude people who are: (i) asymptomatic; (ii) at risk of a disease but unaware of their status; (iii) symptomatic but have not sought help; (iv) have been diagnosed with a disease but have not attended regular check-ups; or (v) have died without being diagnosed.Health examination survey data showed excessive sodium excretion, a marker for salt intake 24 The Department for Health in England set targets in 2006 and worked with the food industry to reduce the salt content of the processed food products that contributed most to the population's salt intake, as identified through health examination survey data (the initial focus was therefore on bread) Policy & practice diabetes and hypercholesterolaemia; and (iii) to assist in the formulation and evaluation of consequent policies.
In addition, health provider-led data sources may introduce bias.The probability of being systematically recorded in a health-care database, or coded in a standardized registry, is influenced by variables that affect access to care, such as age, sex and socioeconomic and geographical characteristics -variables that are also known health determinants.Consequently, administrative data and individual health records may be biased in ways that make health inequalities appear less severe.Moreover, on occasion, provider-based financial incentives may introduce additional biases. 50e could argue that implementing a mandatory national notification system for chronic diseases could attenuate some of these problems.In fact, this type of surveillance has been used for communicable diseases (e.g.acute meningitis infections or chronic HIV infection) for decades with good results.However, mandatory registries

Setting the agenda Policy formation Policy evaluation
Italy 24-hour urine samples taken in an health examination survey showed higher than recommended daily salt consumption in the adult population 25 As a result, the health ministry, in collaboration with NGOs, undertook health promotion actions aimed at increasing awareness of the risks associated with excessive salt intake and reformulated a wide range of products to reduce their salt content in voluntary agreements with the food industry and artisan bakeries

Policy & practice
are useful when disease events are infrequent but not when a disease is highly prevalent or during a pandemic.In addition, mandatory health notification systems and registries are expensive and time-consuming to maintain and validate.Although all medical specialists advocate national registries for their specific diseases, common sense tells us that doctors will not be able to complete standardized notifications for all noncommunicable diseases.Moreover, mandatory registries would not solve the problem of undiagnosed disease.
Another challenge for data collection is that health care is increasingly being provided outside traditional care structures, for example by public-private partnerships or nongovernmental organizations (NGOs) or through technology-based self-management.The result is the absence of integrated care and a lack of data interoper-ability.There is a need, therefore, for universal integrated surveillance of the entire population that would provide data for the design and assessment of population-wide preventive policies and for determining the coverage and performance of individual-based programmes.No matter where the population is receiving care, which health provider is involved (e.g.public, private, a NGO or culturally diverse social services) and whether individuals have adopted a self-help approach, decision-makers should be able to identify the characteristics of the people who are at risk or in need of health services.In addition, governments and health providers must be able to interpret trends in indicators (e.g.coverage of a preventive health intervention or use of a pharmacological treatment for a noncommunicable disease) and to de-termine whether these trends reflect a real change in people's behaviour or risk, or are explained by changes in the places where they seek help or are registered.

External quality control
Data from a prescription information system on dispensed drugs do not tell us which drugs have actually been taken or whether they are working effectively.In contrast, health examination survey data can provide real information about compliance and disease control.Today, the opinions of individuals are more important than ever for guiding health services.As health examination surveys draw information directly from a random sample of both users and non-users of health services, they can act as external quality controls for the entire health system.Moreover, as data are not obtained

Setting the agenda Policy formation Policy evaluation
Finland NA Data from national FINRISK studies linked to national health-care data sets were used to create the FINRISK calculator for identifying individuals at a high risk of cardiovascular disease and the CAIDE risk score for predicting the subsequent development of dementia Recently there has been some concern that the decreasing response rates observed in health examination surveys in high-income countries may affect their external validity.However, even though response rates are decreasing, they remain higher than for mail or online surveys.Moreover, if the participants' characteristics and the participation rate are known, study weights can be used to derive nationally representative statistics.When data are obtained instead from several health centres, data quality can be affected by a lack of standardization, interobserver variability or inter-laboratory variations in analytical processes.

Random samples
Although health surveys may change their way of collecting information (e.g. they may become multimodal) and technological advances may improve electronic data capture, the concept of the random sample (associated with a known survey response rate) remains important.Calculations that involve denominators based on the general population are essential for guiding health policy.
Forms of data collection such as open internet surveys and random mobile phone sampling can reach millions of people at a low cost, but response rates cannot be estimated adequately.Moreover, uptake is low (response rates are generally below 30%) and these methods are prone to several selection biases associated, for example, with digital literacy, access to digital technologies or socioeconomic factors.In one project forecasting obesity in Europe, 51 the researchers noted that data quality across the continent was highly variable and that fewer than half the countries involved possessed nationally representative, objective data.In addition, random sampling is not possible in open internet surveys because participants are all volunteers.As a result, information on event frequency is obtained only from respondents and true population prevalence rates remain unknown.
The most important characteristic of health examination surveys, in contrast, is their external validity, which enables their findings to be directly applied to the population from which their sample was drawn.When adequately powered, health examination surveys can reveal true heterogeneities in risk factor exposure and inequalities in disease burden throughout the population, which can guide the targeting of subgroups during policy development and implementation.Moreover, as health examination surveys use standardized methods, comparative analyses across countries can be performed, including analyses for Global Burden of Disease studies.
Although information technology and artificial intelligence can help develop new sampling frames and better electronic data capture systems, they cannot fix a non-random sample or non-standardized measurements of risk exposure (e.g.different definitions of a smoker) or disease prevalence (e.g.different definitions of hypertension).Consequently, non-standardized data cannot be adjusted for use in timeseries analyses.

Future directions Governance
To aid quality assurance and transparency, health examination surveys should be outsourced by government health authorities, and executed by independent institutions or academic groups whose unedited final reports and databases should be openly shared with the community.Some governments (e.g. in the United Kingdom) use a tendering process for a series of successive health examination surveys to promote long-term investment by universities, survey providers and laboratories.This type of health examination survey governance stimulates positive developments, including: (i) additional fund-raising by, and collaboration between, universities; (ii) continuous training of field teams and standardization of processes and procedures; (iii) the avoidance of precarious working conditions for survey staff; (iv) career development for research assistants and field staff; (v) investment in technological support for surveys; (vi) investment in the validation of new disease screening instruments (e.g.laboratory tests, examination devices and questionnaires); and (vii) opportunities for teaching and research development.
Legislative support for health examination surveys is also needed.Few countries have a track record of regular wide-ranging health examination surveys, and even fewer have secured their continuity by law.Laws should link health examination surveys directly to the iterative process used by health authorities to establish 5-or 10-year health objectives.
Using some health examination survey indicators to assess government objectives in different sectors (e.g.transport, employment, sports and physical activity, social welfare or the environment) could help promote intersectoral policy coordination and a systems-forhealth approach.In addition, such linkages could help justify the financing of health examination surveys.

Financing
Objective assessment of the impact of noncommunicable disease surveillance on health policy development, and of the avoidable costs of noncommunicable diseases could help governments justify their budget for health examination surveys.To date, however, little evidence has been disseminated about the usefulness or impact of health examination surveys or about factors influencing the effectiveness of health examination surveys.Global health initiatives should advocate that every low-resource country has its own health examination survey, and should include financing for these surveys.Initiatives like those developed for global vaccine availability during the coronavirus disease 2019 (COVID-19) pandemic could be established to combat the noncommunicable disease burden and could include: (i) international training for health examination survey project leaders; (ii) the translation of video training material for fieldworkers; and (iii) the low-cost availability of devices used in the field, laboratory materials and the point-of-care analytics used for biophysical examinations.

Methods
Technical support and efforts to standardize surveillance methods, such as WHO's STEPS model and DHS initiatives, are useful and should strengthen low-and middle-income countries' ability to collect data on noncommunicable disease indicators.The availability of guidelines on using the results of health examination surveys to support the additional studies needed in the health planning cycle ( Policy & practice amination surveys should be conducted annually or less frequently, or become a continuous programme must be made on a country-by-country basis and take financial restrictions into account. There is space to improve, and invest in, the technologies used in the field, such as digital data capture; telephone surveys; digital disease screening (including the use of images); laboratory techniques for easier biological sampling; home-based self-sampling or self-examination; and point-of-care laboratory analytics.In the future, health examination surveys could make use of new cancer risk biomarkers, of easier and less expensive biochemical assessments of nutritional status in the general population, and of new environmental exposure biomarkers.
All health examination surveys should be designed to include consent for data linkage with vital statistics and health records.In addition, to increase analytical capacity, ministries of health should develop adequate anonymization techniques and ensure data sets are freely available.The use of standardized questions and protocols in surveys will enable comparative analyses to be conducted over time and across countries.Response rates in household surveys could be increased through social marketing and by improving community literacy, both activities that could also be supported by global initiatives.

Conclusions
In this paper, we have added technical arguments to the debate about the importance of health examination surveys and their continued use during the postpandemic health financing crisis, and in the context of a technological innovation boom that offers new ways of collecting and analysing individual health data.These technical arguments demonstrate that health examination surveys make an irreplaceable contribution to the local availability of primary health data that can be used in a range of further studies (e.g.burden-of-disease, cost and policy impact studies) which are essential for informing several phases of the health planning cycle (e.g.surveillance, prioritization, resource mobilization and policy development).There are solid reasons why health provider-led data sources cannot replace health examination surveys: they may underestimate morbidity and are susceptible to several types of bias.Moreover, the use of nationally representative, random samples of the general population is crucial for maintaining the external validity of any survey.In addition, health examination surveys can provide an external quality control for a country's health system, thereby helping to ensure that the health authority's expenditure is transparent and accountable.In the future, fieldwork for health examination surveys will probably be improved by incorporating technological innovations.

Table 1 . Contribution of national health examination survey data to other study types essential for noncommunicable disease health planning Study type Data contributed by national health examination surveys to other study types Health examination survey indicator Risk factor prevalence Self-reported diagnosis Objective disease prevalence Self-reported treatment and drug use Biophysical param- eters and disease control status Perceived health and quality of life
DALY: disability-adjusted life-year; NA: not applicable; QALY: quality-adjusted life-year; YLD: year lived with disability.Bull World Health Organ 2024;102:588-599| doi: http://dx.doi.org/10.2471/BLT.24.291783Paula Margozzini et al.National health examination surveys

Table 2 . Examples of the influence of health examination surveys on dietary policy, Chile, England, Finland, Italy, Malta, Mexico, Peru and the United States, 1994-2020 Health topic and country Stage at which health examination surveys influenced dietary policy a Setting the agenda Policy formation Policy evaluation
included: (i) a ban on television and online advertising of foods high in fat, sugar and salt before 21:00; (ii) restrictions on price promotions for these foods; (iii) restrictions on where shops may display these foods and unhealthy drinks; and (iv) a mandate for energy labelling of food in restaurants.These proposals were assessed during development of the obesity strategy using Health Survey for England anthropometric data in a Department of Health and Social Care calorie model that explored the likely impact of these and other possible policy Encuestas Nacionales de Salud (National Health Surveys), the Health Survey for England, National Health and Nutrition Examination Surveys and national FINRISK studies are all health examination surveys.

Table 3 . Examples of the influence of health examination surveys on health-care policy-making, Chile, England, Finland, Italy, Malta, Mexico, Peru and the United States, 1994-2020 Health topic and country Stage at which health examination surveys influenced policy-making a Setting the agenda Policy formation Policy evaluation
NA (continues. ..)Bull World Health Organ 2024;102:588-599| doi: http://dx.doi.org/10.2471/BLT.24.291783Paula Margozzini et al.